What is the pH level for tropical fish?

That depends on the type of fish your keeping.

As a general rule tetras and corydora's and angelfish and many others tend to prefer soft (meaning a low amount of dissolved minerals) acidic (meaning pH lower than 7.0) water. 7.0 meaning the water is neutral and neither acidic or alkaline (meaning pH above 7.0).

Most african cichlids species though prefer hard alkaline water. Hard meaning high content of dissolved minerals in the water.

So it's more dependent of the species of fish you wish to keep. The best thing to do is search through google about the type of fish you want. This will often tell you what the best pH range is and which species are compatible.

But I would also point out that fish are very hardy animals given clean living conditions. There is always a maximum low or high point for most fish, but most fish are able to adapt to water conditions that they are not native to.

But for some species pH is almost a must. Like I said just do your research on the species you want to keep, and you'll get more specific answers.